1. Field of the Invention
The present invention relates to a cementless acetabular cup for canine hip replacements; and, more particularly, to an acetabular cup having an inner surface in sliding contact with a femoral head and an outer surface firmly bonded to underlying bone cavity, for providing both initial stability immediately after surgery and long-term stability.
2. Description of the Prior Art
Many patents address issues related to hip replacement, and more particularly to acetabular cup replacement devices. These patents disclose methods for attaching the acetabular cup into a bone cavity using cements of various formulations or screws and barbs in cementless procedures. A number of these patents address primarily human hip replacements, while a few of the patents are directed to canine hip replacement. There exist significant differences between acetabular cups designed for human hip replacement and those used for canine hip replacement. These differences are in large part occasioned by the larger overall weight of a human body, as compared to that of a dog. They also result from the additional attachments needed for human hip replacement devices, and the structure needed the enhanced movement requirements of a dog, which oftentimes spreads his hind legs when lying on its stomach. Accordingly, the geometry of an acetabular cup appointed for canine use is required to be different.
U.S. Pat. No. 4,666,450 to Kenna discloses an acetabular cup assembly prosthesis. The prosthesis comprises, in combination, a support shell for introduction into an acetabulum and a socket insert in nesting engagement within the shell. A support shell is composed of a Co—Cr—Mo alloy. A socket insertis composed of a high-density polyethylene. Both the shell and the anchoring posts are held in a tight fit. Methyl methacrylate is used as a cement, with the result that the device disclosed by the patent is not a cementless acetabular cup assembly prosthesis.
U.S. Pat. No. 4,715,860 to Amstutz discloses porous acetabular hip resurfacing. The device is appointed for human use. An acetabular cup has an outer diameter of 46 to 51 mm and uses a titanium shell with plastic insert. The polyethylene insert is prevented from rotation by use of a pin and metal tabs as well as a peripheral recess. This arrangement relies on point contact between the plastic insert and the titanium shell. It is incapable of preventing movement of the insert with respect to the titanium shell due to flexing of the plastic insert under load. In addition, the cylindrical portion at the sidewall is used to anchor the cementless porous acetabular cup in the bone cavity; the titanium shell is not tightly fitted in the bone cavity. Thus, the titanium shell may rotate within the bone cavity, compromising initial stability. Moreover, bonding of the porous layer applied is oftentimes not coherent. A metallic ring is relied upon to prevent the spilling or dislodgment of the sintered powder compact when the porous acetabular cup is inserted. The acetabular cup disclosed by the '860 patent is appointed for human, not canine use.
U.S. Pat. No. 4,904,265 to MacCollum discloses a cementless acetabular implant for human use, wherein the pelvis is eroded and requires rebuilding. A rigid metallic hemispherically shaped support cup is adapted for contiguous reception with the bone within the acetabular cavity. Reliance is placed on proper drilling of a bone cavity in an excessively eroded bone. The implanted device is progressively matched with the bone cavity. The acetabular cup is attached using a plurality of screws, and relies on these screws to provide initial stability. No disclosure is contained within the '265 patent concerning a canine acetabular cup.
U.S. Pat. No. 5,047,056 to Kenna discloses a canine hip prosthesis. The disclosure is directed to the femoral portion of a canine prosthesis. Use of a porous coating is said to result in superior bone ingrowth. No disclosure is contained by the '056 patent concerning a canine acetabular cup.
U.S. Pat. Nos. 5,226,917 and 5,310,408 to Schryver discloses an acetabular prosthesis with anchoring pegs. The acetabular cup prosthesis has a cup body with a plurality of bores extending between an inner concave surface and an outer convex surface. The bores function as drill guides for providing alignment in the drilling of surgical openings after the acetabular cup body is placed in a patient. The cup body has a porous coating, but is not held in place by interference. Rather, in accordance with teaching of the patents, the cup body is held in place by many drilled pegs, which firmly attach the cup body to the bone. Intimate contact is thereby provided between the cub body and cavity drilled bone. No disclosure is contained within the '914 and '408 patents concerning the cup body's compostion.
U.S. Pat. Nos. 5,290,315 and 5,370,704 to DeCarlo discloses an oblong acetabular cup wherein the plane of the opening into the cavity is skewed relative to the longitudinal plane of the prosthesis. With this arrangement, there is achieved adduction correction, anteversion correction, or both adduction and anteversion correction. This device is for humans with failed hip joint due to loosening of the spherical bone cavity, and requires an oblong acetabular cup. Surgical instruments and surgical methods for implanting the prostheses are disclosed. This correctable acetabular cup is not attached to the bone cavity by use of screws drilled through apertures. The plastic insert is not permanently attached to a block body and is movable by different adjusting elements. This human acetabular cup is appointed for use when the bone cavity is damaged. It is not a canine acetabular cup.
U.S. Pat. No. 5,549,701 to Mikhail discloses an acetabular cup for use by humans in direct-cemented implantation with the bone, or as an insert for a metal shell component of an acetabular cup assembly. This human hip device has a shell, which is attached to a bone with reamed cavity using screws and cement. The high molecular weight polyethylene polymeric cup is attached to the metal shell by means that comprise a pair of dovetail slots, each having a rear wall. Attachment of the cup to metal shell is not permanent. Bone cement and screws that drill into the bone are used to attach the acetabular cup. No disclosure is contained by the '701 patent concerning a canine acetabular cup.
U.S. Pat. No. 5,766,260 to Whiteside discloses an acetabular device for a hip replacement system having an acetabular shell, and a liner having a seal for insertion into the acetabular shell. Upon insertion of the liner into the shell, the annular ridges of the liner come into sealing engagement with the smooth tapered surface of the shell, preventing migration of debris along an interface of the liner with the shell. The liner is provided with several peripheral tabs, which produce an interference fit with several peripheral notches in the shell. A positive engagement is thereby provided to hold the liner in the shell as it bottoms therein. The metallic shell is attached to reamed bone cavity using screws; but is not attached by interference fit. Moreover, the polymeric liner is not firmly attached in any manner, and is not anchored to prevent torsional rotation. It is merely snapped into grooves in the metallic shell using projections in the liner. This is a hip joint replacement implant device for humans and is not appointed for canine use.
U.S. Pat. Nos. 5,874,123, 6,203,844 and 6,558,428 to Park discloses a polymeric prosthesis precoated with a bone cement compatible polymer, which can be polymethyl methacrylate. Once bonded to a polymeric prosthesis, the precoat strengthens the interface between a bone cement and a prosthesis, forming a stiffness gradient when the prosthesis is later implanted. The precoat is said to decrease the likelihood that the prosthesis will loosen and break away from the cement over time. The polymeric implant product appointed for use as an acetabular cup or a tibia plateau in replacing hip joints and knee joints respectively. No disclosure is made concerning cementless incorporation of the implant; the implant is not available for immediate usability, since time is needed for copolymerization.
U.S. Pat. No. 5,876,446 to Agrawal discloses a porous tissue-mating surface prosthesis. A biodegradable polymer impregnated within the interstitial spaces of the surface provides for enhanced rigid fixation and bony ingrowth. No disclosure is contained by the '446 patent concerning a canine acetabular cup.
U.S. Pat. No. 5,879,404 to Bateman discloses an acetabular cup and method for its manufacture. The acetabular cup has an outer shell and an inner liner that provides a bearing surface of metallic or ceramic material. A shoulder, formed around the rim of the inner liner, is made of a material that is softer than that used for the head or neck of a femoral component with which the acetabular cup is to be used. The shoulder limits the motion of the femoral component during use. It is composed of a polymeric material such as polyethylene. The polymeric shoulder of the outer shell is molded directly around the ceramic or metallic inner liner. The acetabular cup uses a polymeric outer shell, which comprises an inner liner of hard metallic or ceramic material and a soft polymeric lip. The polymeric outer shell is directly bonded to the bone cavity. No disclosure is contained by the '404 patent concerning a device for canine use. The device disclosed by the '404 patent does not provide immediate usability since the bond between the shell and bone cavity needs to cure.
U.S. Pat. No. 5,879,405 to Ries discloses an acetabular cup body prosthesis. The acetabular cup prosthesis has a cup body having inner convex and outer concave surfaces. The outer convex surface is not completely hemispherically shaped, but rather has a toroidal shape. A toroidal outer surface of the cup gradually thickens continuously from an apex toward a plurality of points designed to provide interference fit with a bone cavity reamed in a hemispherical shape. The oversized cup has either a toroidal geometry or a two-curvature geometry adapted to create an interference fit with the bone cavity. Interference between the acetabular cup and a spherical bone cavity is accomplished by either the toroidal geometry or the two-curvature geometry of the acetabular cup. Such interference alone is inadequate to securely attach the implant. Accordingly, the device uses screws to attach the acetabular cup. The size of the acetabular cup used in humans is large when compared with the quantum of interference (i.e. 1.25 mm) provided. The implant disclosed by the '405 patent requires an acetabular cup having a size (i.e. 40 mm to 80 mm) that is too large to be used as a canine acetabular cup.
U.S. Pat. No. 6,152,961 to Ostiguy discloses an acetabular prosthesis assembly with a shell component that is implantable within bone and a liner component that is matable to the shell. A groove is formed in the inner surface of the shell and one or more positive surface features are formed on the outer surface of the liner, adapted for selective mating with the groove of the shell. The liner may be joined to the shell by press fitting the two components together such that the positive surface features engage the groove. The shell is attached to the bone cavity by use of screws through a plurality of holes. Protrusions and ridges encourage attachment of the shell and are said to create ingrowth of bone tissue. The prosthesis assembly disclosed by the '961 patent is not a cementless attachment device; but relies instead on screws to hold the device in place. In addition there is no disclosure concerning a canine acetabular prosthesis assembly.
U.S. patent application Ser. No. 2003/0050705 to Cueille discloses an acetabular cup adapted for use in a total hip prosthesis. It comprises a prosthetic femoral head, sized to correspond to the anatomic head size of a natural femoral head, an inner bearing surface portion constructed from a ceramics material, and an outer titanium shell coated with a hydroxyapatite bone-interface layer. The acetabular cup cannot be used immediately after surgery since bone bond has to be developed prior to load application. Furthermore, the acetabular cup disclosed is not an implant device for canines.
U.S. Patent Application No. 2003/0074077 to Taylor discloses an acetabular prosthesis that comprises an outer portion with a concave inner surface and a convex outer surface; an inner portion within and spaced from the outer portion and having a concave inner surface defining a cavity and a substantially convex outer surface; and flexible connecting means, such as vanes connecting the outer convex surface of the inner portion to the concave inner surface of the outer portion. Such an acetabular prosthesis can exhibit matched compliance between the outer portion and the patient's pelvis while the inner portion accommodates idealized rigidity for artificial articulation components. Flexible vanes connect an outer shell with an inner shell in contact with the femoral head. This flexibility is said to provide idealized rigidity. The inner shell is not in interference fit or rigid attachment with the outer support shell in this arrangement. The device is suitable solely for humans, since large loads are flexibly supported.
There remains a need in the art for canine acetabular cups that can be implanted so that the device is usable immediately after surgery. Also needed is a canine acetabular cup that develops a long-term permanent bond between the implant and the underlying bone structure. Further needed is an acetabular cup device that provides increased flexibility capable of meeting the extended motion requirements of a dog. Even further needed is an implant device of the type described which functions throughout the lifetime of the dog without damage or deterioration.